1. Field of the Invention
The present invention relates to a method and apparatus for preventing a certificate from being forged and altered and authenticating the certificate as the original copy based on the feature of the digital certificate. More specifically, the present invention is to issue the certificate after embedding invisibly a text containing a series of information to authenticate the certificate into the digital certificate, and authenticate and confirm the digital certificate by extracting the information text embedded through the method and apparatus suggested in the present invention and confirming the content of the extracted information text.
2. Description of the Related Art
In advance, “embedding” means that not only a first object is physically arranged in a second object but also the content of the second object using a specific algorithm based on the content of the first object is changed so that the content of the first object can be extracted with the algorithm later used and the second object. In particular, in case where the digital certificate includes an image format (logo or seal image representing an issuing authority, etc.), an information text is embedded into the image and in case where the digital certificate does not include an image format, a transparent image is generated to embed an information text. The information text embedded image is inserted in the certificate. Absolutely, there is no change to the naked eye. In other words, the embedded information text is embedded into the image of the certificate or the generated transparent image based on the content which is included in the certificate so as to make visual distinguishing impossible and is employed for authenticating the certificate after the certificate has been issued. The present invention relates to a method and apparatus for embedding the information text into the image which is included in the certificate. In case where an exterior operation is applied to the embedded text, e.g., the digital data processing such as compression, filtering, re-sampling, cropping and the like is processed, it is easily removed and the authentication of the certificate is decided based on whether said information text exists or not. In case where a third party modifies the content of the information text on purpose, the embedded information text is extracted to find out the changed situation by deciding whether the extraction is possible or not and comparing with content of the first embedded text and deciding whether to be identical or not.
At present, as Internet users have sharply increased, trade of products through an electronic commerce has activated. In the trade of products or online/offline transaction, authentication of the digital certificate has been emerging as an important procedure. It is a tendency that process of issuing a certificate including not only such electronic commerce certificates but also various certificates related to civil affair and certificates issued from each school, etc. has been computerized and electronized. However, the reason why it is impossible to issue a certificate as a digital document at present is a forgery and alternation thereof.
The technique for authenticating the digital certificate includes an authentication function application, blank controlling method, bar code method, etc. In the method of applying an authentication function, suppose that both certificate issuer and holder share a common secrete value S. The authentication function includes a secrete key algorithm, message digest and the like wherein the representative function is a hash function. Authentication using the hash function is proceeded as follows: First, an issuer of certificate of authentication calculates the hash value by the certificate, secrete key value S, and hash function and adds the hash value result to the certificate and sends the certificate to a person who requests to issue a certificate. A person who receives a certificate finds the hash value by the session key S that the person already knows and the hash function. The above hash value is compared with the hash value which is sent from the issuer of certificate of authentication. If the two hash values are the same, its authentication is confirmed and if not, the certificate of authentication is regarded as being altered. Comparison of the hash value enables to confirm identity (authentication) of the other party of the transaction and detect whether the certificate is forged or altered.
Such authentication using the authentication function has the following drawbacks:
First, authentication is based on a text document. If a document of different format such as an image or voice mark is embedded into the certificate, it should be separately authenticated or its authentication is impossible.
Second, it can accurately determine if the document data has been modified. However, if modified, it is impossible to restore the original document.
Third, since a signature should be added so as to confirm integrity of the certificate of authentication, the size of the original certificate has been enlarged.
The authentication method using a blank controlling method or letter-form controlling method is based on ASCII code. The ASCII includes 94 picture characters and 34 various characters which are only used for controlling but not printed out. The picture characters include 26 capital characters, 26 small characters, 10 numbers and 32 special characters (%, *, $, etc.). The 34 controlling characters are employed for controlling the destination of data as the standard already designated and arranging texts to be printed out. The controlling character is classified as the following three types of characters, i.e., format effector, information separator, and communication-control character. The format effector controls the layout of print-out and includes familiar controls for a type such as backspace (BS), horizontal tabulation (HT), carriage return (CR). The information separator is used for dividing data into a paragraph or page and includes record separator (RS), file separator (FS), etc. The communication-control character is used for preparing format in which a text message is conveyed through a phone line such as STX (start of text), ETX (End of Text), etc. Most of computers deal with a unit of byte as amount of 8 bits. Hence, ASCII character is mostly stored one by one each byte. The remaining one bit is used for a different purpose if necessary. For example, a printer sets up the highest effective bit as 0 and separates ASCII as 8 bit. The blank controlling method or letter-form controlling method, using such controlling character, controls the blank of the text document of the original certificate to express the information to be embedded or changes the letter-form to express the embedding information. In case where the user's information is embedded on the object of the above code of the document, the drawbacks are as follows:
First, the text document itself of the substantial certificate is changed. The change itself is not shown in the document. Hence, in case the document is again restored after having been changed, a restoration signal is definitely damaged. That is, it is impossible to perfectly restore the text document.
Second, the region wherein a user can embed the information is small. It can not but embed the information that a user wants in a restricted manner.
Authentication using the bar code method is at present actively applied. The bar code is a code system expressing the information with a pattern of arrangement of black bar and white bar having various widths. Use of bar code makes it possible to deal with office work in an effective, fast, and accurate manner. As its effective value has been admitted in the nation, it is used in various fields of affairs such as office automation, factory automation, etc. around the distribution industry. At present, various ID card employs the bar code. For a student card, the bar code employed therein has a card recognized in a card recognizer when students come in and out the library and a recognition apparatus recognizes the bar code, thereby confirming authenticity of ID cards and identity information. However, such authentication using the bar code has the following drawbacks:
First, the bar code is a code system expressing the information with a pattern of arrangement of black bar and white bar having various widths, thereby making it possible to discriminate it with the eye and thus its alternation is possible.
Second, even though the bar code is scanned many times, failure to read the bar code leads to inputting numbers using a keyboard.
Third, if the bar code is uncertain or is damaged during the distribution, a scanner may read it as wrong numbers.